(a) Field of the Invention
The present invention relates to an apparatus and a method of measuring feeding velocity of a web by using an encoder.
(b) Description of the Related Art
Recently, a technology for producing low-cost consumable electronic device products, such as radio frequency identification (RFID), a solar cell, and electronic paper, having accuracy of a level or several to several tens of micrometers by using a printing process on a flexible substrate (web) has been suggested.
To this end, a plastic substrate is used instead of a high-priced silicon wafer in view of a material, and a low cost process of performing direct printing at a low temperature, such as an inkjet process, a gravure printing method, and a screen printing method, has been researched in terms of a process, and a roll to roll printing process has recently become a consideration for maximizing productivity compared to an inline supply method.
In this case, the roll to roll printing method is a contact-type printing method of coating ink on a printing roll, and directly transferring the ink to a substrate (hereinafter referred to as a “web”) formed of plastic or a thin metal film, and includes a gravure method, a flexography method, an off-set method, and the like.
A technology necessary for the roll to roll printing process and equipment technology development generally includes a printing process equipment technology, a roll to roll web feeding control technology, and the like.
In this case, in order to print a precise pattern on the web, velocity of the roll needs to be matched with feeding velocity of the web. When the velocity of the web is not matched with the velocity of the roll, the pattern printed on the web may overlap, or may be printed at a position other than where the pattern needs to be actually printed.
In this case, in order to measure the feeding velocity of the web, a method using a linear encoder is suggested in the related art as illustrated in FIGS. 1 and 2.
FIG. 1 is a conceptual view illustrating an apparatus for measuring web feeding velocity by using an encoder in the related art, and FIG. 2 is a conceptual view illustrating an apparatus for measuring web feeding velocity by using a 4-field encoder in the related art.
As illustrated in FIGS. 1 and 2, the apparatus for measuring web feeding velocity according to the related art includes a web W on which a scale S is formed and a mask R disposed on the web W to allow light to pass through at a specific pitch, and a detection unit measures a change in intensity of light passing through the scale S and the mask R to measure the feeding velocity of the web W.
In this case, the feeding velocity of the web is calculated by forming a Lissajous circle by using the change in the intensity of light measured by the detection unit, and then calculating a specific angle of the Lissajous circle.
However, it is difficult for the apparatus for measuring web feeding velocity according to the related art to measure feeding velocity of the web in the case where a scale pitch or a line width of the web W is changed. More particularly, the apparatus for measuring web feeding velocity according to the related art measures a change in intensity of light for each of four phases, and in this case, when a pitch of a scale or a line width corresponding to each phase is not matched, it is difficult to accurately calculate feeding velocity.
Further, in the case where a change in a pitch is small, measurement accuracy is decreased, and when a change in a pitch exceeds a predetermined level, a degree of signal distortion is increased, so that measurement itself is impossible.
The apparatus and method for calculating feeding velocity of a web by using a signal for each of the four phases described above are described in related art literature below in detail, so detailed descriptions thereof will be omitted.